Means for adjusting the flow characteristics of fluid flow machines



JF, G .orA

Nov. 24, 1959 R A NOVAK 2 914,241

t n MEANS FOR ADJUSTING THE FLOW CHARACTERISTICS OF FLUID FLOW MACHINESFiled NOV. 50, 1955 Maisy/Mme@ IV//l//l/A United States Patent MEANS FORADJUSTING THE FLOW CHARAC-4 TERISTICS OF FLUID FLOW MACHINES RichardAugust Novak, Wyoming, Ohio, assignor to General Electric Company, acorporation of New York Application November 30, 1955, Serial No.550,123 Claims. (Cl. 230-114) The present invention relates to means foradjusting the flow characteristics of lluid flow machines and moreparticularly to means for varying the ow characteristics of multi-stagedcompressors in accordance with rotational speed.

In present gas turbine engines ofthe type used in aircraft, the demandfor increased thrust is conveniently met by providing a high pressureratio compressor. Such engines are usually designed to function mosteiciently in the upper portion of the speed range, so the shape of thecompressor duct and the shape and incidence of the compressor bladingare chosen for ecient operation at cruise or maximum power conditions.When a conventional high pressure compressor is designed under theseconditions, it has been found that severe diiiiculties are encounteredin operation over the lower portions of the speed range due to stallingof the blades in the inlet stages of the compressor. To alleviate thiscondition it becomes desirable to vary the flow characteristics of thecompressor to correspond to the operating speed of the engine. This isaccomplished by adjusting the angle of attack of the compressor bladingin accordance with the design requirements of the various operatingspeeds, thus permitting eflicient operation of the compressor over theilow speed range. In achieving the desired adjustment it is known to bebeneficial to vary the orientation of the stator blades in the inletstages and the usual practice is to adjust the entire blade. Thispractice has the disadvantage of changing the flow characteristics overthe full length of the blade, whereas the most troublesome stallingconditions occur only at certain portions of the blade. In addition,this practice presents mechanical difiiculties due to the relativelylarge torques required to turn the blades plus the complicated blademountings required.

The present invention comprehends adjusting the iiow characteristicsover only that portion of the blade length where it is most important byprovision of means for closing down the stator blades in the areasadjacent the outer casing only, and facilitating the use of the normalstator blade shroud construction.

An object of the present invention is the provision of means foradjusting the ow characteristics across the tips of compressor rotorblades in accordance with the design requirements of varying operatingspeeds.

Another object is the provision of means for adjusting the ilowcharacteristics across the tips of compressor rotor blades, said meansrequiring reduced torque to operate and permitting the use of normalstator shroud construction.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Figure 1 is an elevation view partly in section of the inlet stages ofan axial llow compressor embodying the present invention;

ice

" on lines 2-2 of Figure 1;

Figure 3 is an elevation view partly in section of an axial ilowcompressor embodying another embodiment of the present invention;

Figure 4 is a sectional view at an enlarged scale taken along lines 4-4of Figure 3; and

Figure 5 is a sectional view of a modiication of the construction ofFigures 1 and 2. y

Referring more particularly to Figure 1A of the drawing, the compressorconstruction shown includes an outer casing 11, an inner casing 12 andalternate rows of stator and rotor blades 13 and 14 respectively. Eachstage of stator blades is fitted with a circular shroud 15 atthe tipsthereof. The shrouds provide support for the tips ofthe j stator bladesand maintain the desired spacing between adjacent blades. A tab 16ismounted closely adjacent to and downstream of each stator blade. Eachtab is of right triangular construction and is pivotally mounted ontheouter casing and the shroud with its base adjacent theA outer casing andits apex adjacent the shroud, so that the leading edge of the tab isparallel with the trailing edge of the adjacent stator blade. The apexof the tab is connected to the shroud by means of pin 17 and the base ofthe tab is connected to the inner casing by means of the pin 1S whichextends through the casing and is secured to crank arm 19.

As shown in Figure 2, each tab is mounted inline with ythe adjacentstator blade and is adapted for pivotal movement towards the pressureside of said blade to the dotted line position. n v

The conguration illustrated in Figure 3 includes an outer casing 21 andan inner casing 22 stator blades 23 and rotor blades 24. A shroud 25 istted at the inner ends of the stator blades joining the tips thereofmaintaining them in spaced relation. A triangular shaped tab 26 ismounted at the downstream edge of each stator blade and forms thetrailing edge thereof. As in the embodiment of Figure l, the tab 26 ispivotally mounted on the inner casing andthe shroud by means of thepinf28 and 27 respectively. Crank arm 29 is connected to pin 23 at theouter surface of the outer casing.

As shown in Figure 4, the tab 26 forms the trailing edge of the statorblade 23 and is movable toward the pressure side thereof as indicated inthe dotted line position.

The showing of Figure 5 is a modification of the construction of Figures1 and 2, wherein a tab 31 is mounted downstream of and between adjacentstator blades 32 and 33. The tab is pivotally mounted on the outercasing and the shroud and is not positioned in line with the statorblades, but instead is laterally offset from the stator blade 32.

In the operation of the present invention the tabs are rotated to closedown the compressor by deilecting the ilow of working uid through therotor blade stages adjacent the outer casing. When the compressor isoperated at speeds less than the designed speed, the axial velocity lofthe working uid adjacent the inner casing is reduced more sharply thanthat adjacent the outer casing,

thus creating an energy gradient extending diagonally downstream betweenthe inner casing and outer casing. This energy gradient increases as thellow of tiuid progresses from one stage of rotor blades to anothercausing an increase in ow adjacent the outer casing and a decrease inflow next to the inner casing until the axial velocity of ow adjacentthe inner casing approaches zero, at which point stall occurs. Toprevent the development of these stall conditions the present inventionreturns the energy gradient to a radial position between the innercasing and the outer casing. This is accomplished by movement of thetabs, causing a transfer of energy from `the outer casing to.the innercasing so that the energy gradient is sharply decreased and is returnedto a radial position. When the 'tabs are moved towards the pressure sideof the adjacent blades, the ow of working fltid is 'dee'ted or turnedsuch that the ratio Vof its 'rotational velocity to its axial velocityis increased adjacent the outer easing. In addition, a portion of theo`W of working uid is displaced inwardly by the tabs so that the axialvelocity is increased adjacent the inner casing. The stall generatingconditions characterized by the diiic'erence in axial velocitiesadjacent the inner and outer casings are thus o'vercor'ne.

The tabs in a single stage may be operated simultaneously b'y means ofthe crank arms I9 and 29 as a function of compressor speed. The amountof turning in 'a single stage will vary with operating speed and ifdesired the anount of 'tlriing' may be varied from stage testage for asingle speed.

lThe tabV constructions' illustrated -in "Figures 2, 4 and 5 all operatein a similar mann/er to cause a vtransfer of energy from lthe otereasing 'to the inner casing and reduce the diiferent'i'alhetween'theaxial velocities of working' tluid adjacent the o'uf'er' andinner casings. The tab arrangement of Figure 2 isV slightly moreefticient in turning the working duid -since the space between thestator blade and the tab acts as a vboundary layer bleed duct to drawolf the suction side boundary layer air. In addition, the constructionof Figures 2 and 5 permits the use of conventional stator blades.

While particular embodiments of lthe invention have been illustrated anddescribed it will be obvious to those skilled in the art vthat variouschanges and modifications may be made without Vdeparting from theinvention and it is intended to cover inthe appended claims all suchchanges and modifications that come within the true spirit and scope ofthe invention.

What is claimed is:

1. In a multi stage compressor 'including' an inner casing, an outercasing and alternate stages of stator and rotor blading, at least onestage of stator blades being shrouded the improvement Consisting oflongitudinally tapered tab pivotally mounted between the shroud andouter 'casing downstream of ea'ch stator blade, each of said tabsextending over the full length of the adjacent stator blade and having alarger chord at the outer casing than'at the inner casing. o

2. In a multi stage compressor including an inner casing, an outercasing and alternate stages of stator and rotor blading, the improvementconsisting of an air foil shaped tab extending between the inner andouter casings downstream of each stator blade and pivotally mounted onat least the outer casing, the leading edge of each tab being parallelwith the trailing edge of the adjacent stator blade, and the trailingedge of each tab diverging from the leading edge thereof from the innercasing to the outer casing.

3. In a multi stage compressor including an inner casing, an outercasing and alternate stages of stator and rotor blading, atleast onestage of stator blades being shrouded the improvement consisting of anair foil shaped tab pivotally mounted between the shroud and outercasing immediately downstream fof -each stator blade, the leading edgeof'each tab being parallel with the trailing edge of the adjacent statorblade, and the trailing edge of each tab diverging from the leading edgethereof from the inner casing to the outer casing, each tab beingpivoted at its leading edge, and the trailing edge of the tab taperingyfrom a very smalllchord at the inner casing to a relatively large chordat the outer casing.

4. In a multi stage compressor as defined in claim 2, wherein each tabis positioned-in line with the adjacent stator blade.

5. In a multi stage compressor as dened in claim 1, wherein each tab isoffset laterally from the adjacent stator blade.

References Cited in the leof this patent UNITED STATES PATENTS 1,544,288Van'Ormer e June 30, 1925 1,622,930 Von Karman et al Mar. 29, 19272,314,572 ChitZ Mar. 23, 1943 2,337,861 Adamtchlk Dec. 28, 19432,412,365 Sollinger Dec. l10, 1946 2,606,713 Bauger Aug. 12, 1952v2,648,390 De Lagabbe Aug. l1, 1953 2,689,680 Lovesey Sept. 21, 1954

